Under certain conditions progestins have been shown to stimulate the growth of the human breast cancer cell line, T-47D. The overall aim of this proposal is to determine the mechanisms of progestin induced growth stimulation. Preliminary studies from this laboratory have indicated that under the above conditions, progestins increase the level of c-myc mRNA. The current proposal aims to understand how progestins do this. Four specific aims are listed:1. To determine if the increase in c-myc mRNA is a primary response to progestins i.e is it independent of protein synthesis. 2. To determine if a functional progestin response element is present in the c-myc gene.3. To address the question: Is enhanced c-myc expression necessary for progestin induced proliferation? 4. To address the question: Why is c-myc responsive to progestins in T-47D cells but not in MCF-7 cells, which are both progesterone receptor positive?